In U.S. Pat. No. 3,733,499 a crystal of thallium arsenic selenide, Tl.sub.3 AsSe.sub.3, is described for use in a pyroelectric detector. While crystals of thallium arsenic selenide have excellent nonlinear optical properties, it is difficult to make quality crystals of the material because of its softness. During growth, crystals of thallium arsenic selenide can exhibit a variety of macroscopic defects including cracks, precipitates, inclusions, voids, striations, and compositional inhomogeneity depending upon the growth parameters employed. Lengthy and careful optical polishing and fabrication techniques are required to provide crystals that are free from significant flaws. Improvements in optical scattering losses and optical homogeneity are required before the full capabilities of this material can be realized in various optical devices.
The main object of this invention is to produce crystals of thallium arsenic selenide, thallium arsenic sulfide, thallium vanadium sulfide, thallium phosphorous selenide, lead halides, cadmium sulfide, cadmium selenide, cadmium tin arsenide, cadmium germanium arsenide, indium phosphoride, indium arsenide, and the like, and mixtures thereof, that have superior physical and optical properties and are easier to fabricate.